Tektronix 7633 Oscilloscope Repair

[KWKolb]

I am about to embark on a repair of my 7633 and was hoping someone could help point to the cause.  I have both the Operator's and Service Manuals on hand.

The display shows anomalous traces.  Also, the scope makes a faint intermittent buzzing noise when warming up.  The fan slows while the scope buzzes.  The buzzing and traces occur with or without plug-ins installed.  The traces change somewhat depending on the time base setting.  Pictures below showing two different time base settings and with plug-ins removed.

Thank you in advance for any assistance you can provide.

[tecman]

Likely power supply electrolytic caps.  Known problem as they age.  Replace them all.

paul

[David Hess]

I agree about the aluminum electrolytic capacitors in the power supply.

Start with the procedure in the service manual for checking the low voltage power supply outputs for level and ripple.

[KWKolb]

I checked the voltages and the -15v supply looks almost sawtooth-like.  That points to a 14,000 uF, 25v cap.  If I can find them, I will replace all seven of the big power supply electrolytic.

Now the question is where to purchase large electrolytic  (largest is 18,000uF at 15v) in onesy-twosy  quantities at a good price.

Respectfully,
Kevin

[tautech]

I checked the voltages and the -15v supply looks almost sawtooth-like.  That points to a 14,000 uF, 25v cap.  If I can find them, I will replace all seven of the big power supply electrolytic.

Now the question is where to purchase large electrolytic  (largest is 18,000uF at 15v) in onesy-twosy  quantities at a good price.

Respectfully,
Kevin

I've used these guys for the less popular values:
http://www.tedss.com/

[daveyk]

I checked the voltages and the -15v supply looks almost sawtooth-like.  That points to a 14,000 uF, 25v cap.  If I can find them, I will replace all seven of the big power supply electrolytic.

Now the question is where to purchase large electrolytic  (largest is 18,000uF at 15v) in onesy-twosy  quantities at a good price.

Respectfully,
Kevin

Make sure there aren't any 10uf caps in the feed back or regulator control pins. I would be it's a small one rather than the big ones.

I think that is the same scope I use to use in the early 1980s with a spectrum analyzer module plug-in. We used them to certify ultrasonic transducers. We used a Tektronix camera to take screen shots with Polaroid film. I see the electrical connections for it on the CRT bezel of your scope.

Dave


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[dave_k]

I checked the voltages and the -15v supply looks almost sawtooth-like.  That points to a 14,000 uF, 25v cap.  If I can find them, I will replace all seven of the big power supply electrolytic.

Now the question is where to purchase large electrolytic  (largest is 18,000uF at 15v) in onesy-twosy  quantities at a good price.

Respectfully,
Kevin

Kevin,
Maybe this information might help you...
https://www.eevblog.com/forum/testgear/tektronix-76037613-repairs/msg743296/#msg743296

[David Hess]

Now the question is where to purchase large electrolytic  (largest is 18,000uF at 15v) in onesy-twosy  quantities at a good price.

Respectfully,
Kevin

Usually I end up using snap-in or leaded radial capacitors as replacements even if I have to make modifications because they are relatively inexpensive.  The regulator board is held in place by screws into the chassis and does not rely on the capacitors so this will not be a problem.

A suitable snap-in or leaded radial capacitor to replace the 18,000uF at 15 volt capacitor can be had for less than $5 new.  Do not be afraid to use the next larger standard value like 22,000uF instead of 18,000uF if it is less expensive.

[KWKolb]

Thanks all. Capacitors are on order.  Also ordered some metal feedthroughs to make adapter boards to mate the new snap-in caps to the Low Voltage Rectifier Board.

Will update when I install the new capacitors.

VR,
Kevin